Surgical masks have a lot of bad rep for filtering PM2.5. There’s a fantastic educational poster from Greenpeace that I’ve seen in several places:
It offers great advice on masks that protect us from PM2.5, soot or wildfire smoke. But then it says this this about surgical masks:
“No effect” it says. But when I read the cited articles, I saw no tests of surgical masks on PM2.5.
News outlets have made similar claims. In the US, National Public Radio claimed that surgical masks can “only block large droplets.” They say surgical or medical masks won’t capture tiny coronavirus particles, which measure 0.06 microns to 0.14 microns.
If I give Greenpeace the benefit of the doubt, maybe when they say surgical masks have “no effect” on PM2.5, they really mean “a small effect.” Then how small would be small? 10% of particles? 20%?
Three independent studies convinced me that surgical masks are shockingly good at protecting against particulate pollution, even particles as small as viruses.
1. The Edinburgh Surgical Mask Study
Researchers from Edinburgh University tested how much diesel exhaust different masks could block, including a surgical mask. They tested down to .007 microns. That’s less than 10% of the size of the coronavirus. Yet the surgical mask blocked 80% of particles.
2. Dr. Saint Cyr’s Surgical Mask Fit Test
In Beijing, Dr. Richard Saint Cyr fit tested several masks on his face using a fancy fit-testing machine.
The surgical mask did a bit worse here – 60%. That’s probably because this is a fit test, so it takes into account leakage around the mask.
This isn’t the only test. Surgical masks scored 50% in Smart Air’s fit test of masks in India and 47% in a test in Singapore. Still, 50% is far from “no effect.”
3. U Mass Study on Surgical and N95 Masks
In a study out of the University of Massachusetts, researchers tested N95 masks, cloth masks, and a surgical mask. They tested the masks on a mannequin to mimic effectiveness while a person is wearing it, not just the particle capture rate.
The left-most mask is a 3M N95 mask, the “N95 mask2″ is a Moldex N95, and the right-most mask is a cheap surgical mask bought from a street vendor in Kathmandu. The surgical mask blocked about 60% of .03 micron particles and over 90% of 1 micron and 2.5 micron particles.
Scientific fit tests and particle penetration tests find that surgical masks as cheap as 1 RMB (US$0.15) block between 60-90% of particles. That includes even really small particles and even while a person is actually wearing it.
Should You Wear A Surgical Mask?
Now let me be clear. I’m not recommending that everyone use surgical masks. I wear N95 and N99 masks because tests show they fit better and capture more particles. But there are situations when I might wear surgical masks. If N95 or N99 masks are unaffordable or unavailable; if it’s a bad air day and I forgot my normal mask at home; or even if I’m caught out in a wildfire. Ducking into a pharmacy and spending a few cents on a surgical or medical mask will significantly reduce your exposure to particulate pollution.
WHAT NEXT?
Along with wearing masks, air purifiers with HEPA filters are also one of the best ways to stay safe from a variety of pollutants in our air including viruses and dangerous PM2.5. A recent CDC study confirmed significantly lower COVID-19 infection rates in schools that used HEPA air purifiers. HEPA filters can significantly lower the risk of a variety of deadly diseases including diabetes, heart disease, cancer, and high blood pressure.
Read More: Four Steps to Choosing the Best Air Purifier
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Hey there. I was an early adopter of Smart Air DIY filters 9 years ago, good to see where you are now! I was searching about the ability of different mask options (the various 3M ones, vogmask, airinum etc.) to filter car tyre particles, which made headlines recently as an under-the-radar large source of particles compared to exhaust fumes, and found almost no information. For instance here https://www.theguardian.com/environment/2022/jun/03/car-tyres-produce-more-particle-pollution-than-exhausts-tests-show. Says tyre particles are smaller than 23nm (how much smaller it doesn’t say) and you are saying here that particles of 7nm (0.007μm) are filtered out by masks, so there a chance… Read more »
So would an ASTM level 3 mask block significantly more aerosols than a cheap 3 layer?
Hey Choon, great job and with scientific standard! Better then any public communication.
Greetings from Germany!
I am launching a new foundation to tackle air and soil contamination in Mongolia called Green Belt. I would love to cooperate with you and your organisation. Also, can I have the complete names of the three studies you have referenced at the top in regards to the efficacy of surgical mask in reducing the pollution we breath in. Thank you for the work you are doing and looking forward to hearing back from.